The National Investigation Agency has filed a supplementary charge sheet against four arrested cadres of the Popular Front of India in a case related to the "unlawful and anti-national activities" of the proscribed outfit in Bihar, an official said on Friday, reported news agency PTI.

The fresh charge sheet has been filed in the NIA Special Court, Patna, against Md Tanweer, Md Aabid, Md Belal and Md Irshad Alam, all residents of East Champaran district of Bihar, a spokesperson of the anti-terror federal agency was quoted by news agency PTI as saying.